Thermal management techniques in an electronic device

ABSTRACT

A thermal manager has a digital filter whose input is to receive raw temperature values from a sensor and whose output is to provide processed or filtered temperature values according to a filter function that correlates temperature at the sensor with temperature at another location in the device. The thermal manager has a look-up table that further correlates temperature at the sensor with temperature at said another location. The look-up table contains a list of processed temperature sensor values, and/or a list of temperatures representing the temperature at said another location, and their respective power consumption change commands. The thermal manager accesses the look-up table using selected, filtered temperature values, to identify their respective power consumption change commands. The latter are then evaluated and may be applied, to mitigate a thermal at said another location. Other embodiments are also described and claimed.

RELATED APPLICATIONS

This application claims the benefit of the earlier filing date of U.S.provisional application No. 61/057,767 filed May 30, 2008. Certainsubject matter described in this patent application is related tomaterial in U.S. patent application Ser. No. 12/250,498 filed Oct. 13,2008.

BACKGROUND

Consumers' appetite for more performance and functionality from aportable handheld wireless communications device (such as a cellulartelephone) typically outpaces developments in battery technology and lowpower consumption electronics. Thus, manufacturers of such devices areforced to find better ways of dealing with reduced battery life and hightemperature effects (thermals). Various power management processes havebeen developed as software that runs in desktop and laptop personalcomputers, to better manage the computer's power consumption whileproviding a reasonable level of performance for the user. For instance,so-called low power techniques use display screen dimming and processorclock throttling to lengthen battery life. In other cases, the speed ofa cooling fan inside the computer is modulated, to regulate the internaltemperature of the computer, i.e. control thermal situations in thecomputer. More recently, the power consumption of certain integratedcircuit components in a portable laptop or notebook personal computerhave been controlled or managed, to improve thermal characteristicstherein.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the invention are illustrated by way of example andnot by way of limitation in the figures of the accompanying drawings inwhich like references indicate similar elements. It should be noted thatreferences to “an” or “one” embodiment of the invention in thisdisclosure are not necessarily to the same embodiment, and they mean atleast one.

FIGS. 1-2A are graphs showing simulated thermal behaviors.

FIG. 2B is a block diagram of components that perform a thermalmanagement process in an electronic device.

FIG. 2C is a block diagram of components that perform a moresophisticated thermal management process.

FIG. 3 is an external elevation view of an example electronics device inwhich a thermal management process in accordance with an embodiment ofthe invention can be running.

FIG. 4 is an internal view of different layers of components within thedevice of FIG. 3.

FIG. 5 is a flow diagram of a thermal management process in accordancewith an embodiment of the invention.

FIG. 6 is a flow diagram of a thermal management process in accordancewith another embodiment of the invention.

DETAILED DESCRIPTION

An embodiment of the invention is directed to an improved thermalmanagement process running in a portable handheld wirelesscommunications device that has relatively confined internal space, tomanage the device's own thermal behavior but without significantlyimpacting the user experience. There are at least two relevant aspectsto such a process. First, the behavior of the device is managed so thatthe temperature of the device's battery (or other rechargeable mainpower source) stays within a given predefined range. See, e.g.Certification Requirements for Battery System Compliance to IEEE 1725,October 2007, Revision 1.4 (CTIA Certification Program). This is becausebattery temperature may quickly rise to undesirable levels during evennormal operation of the device, e.g. when using a device that has beenleft inside a parked automobile in the sun, to make a cellular phonecall. In part, this may be due to the operation of certain power hungryintegrated circuit components of the device, such as the RF poweramplifier (PA) that drives the device's cellular network RFcommunications antenna. For example, the RF PA often responds torequests from a base station, with which the device is registered, toincrease its RF output power if the base station determines that signalfrom the device is weakening for any reason. This, together with thenormal current drawn by the remaining electrical components, maysignificantly increase the heat that must be dissipated, due to theelectrical power consumption by the RF PA, thereby causing the batteryto quickly heat up due to its relative proximity to the RF PA.

A second thermal arena to monitor and manage in the device is thedevice's external case temperature. This should also be kept in apredefined range, e.g. as specified by Underwriters Laboratories (UL)for consumer grade cellular telephone handsets. During normal operation,the external case of the device should not become so warm as to becomeuncomfortable for the user, e.g. while it is being held in the usershand or against the user's ear. The external case may be heated by anypower consumed within the device, and the hottest points on the externalcase will most likely be in proximity to the circuitry with the highestconcentration of power dissipation. In one embodiment, this may be theRF PA, as in the example above, or it may be another component or groupof components, such as the application processor in a mobile telephoneor smart phone.

A given mobile device may include more than one source of heat thatindividually, or in concert with others, causes either one or both ofthe battery and the external case temperature to rise above the desiredmaximum temperature. Also, the inventions described in this document arenot limited to managing the temperature of batteries and external cases,but are applicable to any undesirable thermal behavior in the mobiledevice.

In this description, all references to temperature values are in degreescentigrade.

The process of thermal management needs accurate information about thetemperature in various places of the device. For example, multipletemperature sensors can be built into the device, and then calibratedbefore use. These may be in contact with or located near theirrespective components to be monitored. Temperature readings are “sensed”by such sensors, e.g. by passing a known current through a thermistorduring normal operation of the device, measuring its voltage andcalculating its resistance. In contrast, there are also indirectmechanisms that can be used for measuring temperature. For example,during the device's design and testing in the laboratory, the powerconsumption of a component (e.g., a microprocessor) can be sensed over aperiod of time. This type of power consumption and associated timeinterval data can then be correlated with direct temperaturemeasurements of the component taken during testing. A mathematicaland/or lookup table relationship is then derived, which is then storedin the device for later use “in the field”, i.e. normal operation of thedevice by the end user or consumer. While in the field, thermalmanagement decisions can be automatically made in the device, e.g. byexecuting software, based on “effective” temperature readings that havebeen computed or looked up using the stored relationship, as a functionof sensed power consumption measurements.

There are several heat-generating components of the device that may beautomatically controlled, to efficiently improve the thermal behavior ofthe different arenas (for example, the battery and the external case) ofthe device. One is the cellular network RF transceiver PA whose outputRF power can be limited so as to override a contrary request from thecellular base station. Another is a central processing unit (CPU), e.g.its microprocessor clock can be throttled down or its power supplyvoltage may be reduced at the expense of reduced performance. Yetanother is the backlight of the device's main display screen, which canbe dimmed at the expense of reduced display clarity.

In one embodiment of the invention, a “thermal time constant” or thermaldecay parameter may be defined for a given component or area of thedevice. This parameter or function may describe the relationship overtime between (1) the temperature of a given component or target area ofthe device and (2) the temperature of a remote location. The thermaltime constant takes into account the realization that while the outputof a temp sensor could jump to a high value, indicating a fast rise intemperature at that location, the temperature of a remote, targetlocation (that may also be affected by the same increased heat) willrise more slowly (e.g., along a substantially different curve). This isillustrated in the example, simulated temperature response graph ofFIG. 1. This graph shows the simulated behavior of actual batterytemperature (degrees) over time (minutes), responding to a suddenincrease in heat that is producing essentially a step response in theraw temperature data output by a sensor that is remote from the battery.The graph shows the result of processing the raw temp sensor data usingthe appropriate thermal time constant, to yield a somewhatexponential-looking curve. The processing includes a low pass filteringfunction that translates an essentially instantaneous change (from someother temperature to 70 degrees) into a much slower change.

FIG. 1 also illustrates another aspect of thermal behavior in thedevice, namely that the “steady state” temperatures of the sensor andthe target location may be different. Note how the processed temp sensorcurve is similar in shape to the battery temp curve, but not in absolutevalue—70 degrees at the sensor means only 50 degrees at the battery(after about fifteen minutes). To make this adjustment, a furthermathematical function (derived from the processed temp sensor data andthe actual temperature of the target location) can be applied to theprocessed data. Examples of such functions can be seen in equations 1and 2 described below.

While FIG. 1 depicts a simulated step response, FIG. 2 shows simulatedrandom heating occurring in the device. Note how the relatively sharpedges of the raw temp sensor curve have been smoothed out by the thermaltime constant-based processing.

Different components of the device may have different-valued thermaltime constants or thermal decay parameters, which is a function of howquickly the heat produced by the component can be dissipated by thedevice. For example, the CPU may normally be subjected to its peak powerconsumption level for a relatively long period of time before itstemperature reaches an upper threshold (e.g., several minutes). Incontrast, peak RF output power by the cellular network RF transceiver PAcan only be sustained for a much shorter period of time (before an upperthermal threshold is reached). The thermal time constant of a componentmay also incorporate the following characteristics: several, relativelyfrequently occurring and long periods of low power consumption by acomponent can lead to the same elevated temperature that would result ifthe component were subjected to fewer and shorter periods of high powerconsumption. Below are some example time constant parameters for thedevice 100 described below.

TABLE 0 Remote Temperature Correlation Temperature Sensor Location TimeConstant (target location) RF Power Amplifier  15 seconds Battery HotSpot Battery 220 seconds Back Case Center

The table above gives an example for two remote temperature sensors, onelocated near the RF PA and another located at the battery (thoughperhaps not necessarily at the battery's hot spot). There may however bemore than two sensors in the device, e.g. another located on-chip with acellular baseband processor and another located in a different area thanall of the others so as to give a better estimate of the ambienttemperature inside the device, e.g. near a subscriber identity module,SIM, card circuit.

A generic thermal management process or system that uses a thermal timeconstant to compute or estimate the real temperature behavior (over agiven time interval) of a target location (the “correlation temperature”in Table 0 above) is now described. Referring to the block diagram ofFIG. 2B, for a temperature of interest (e.g., that of the battery hotspot or the back case center), output from an associated temperaturesensor 201 is processed using the associated thermal time constant. Thetemperature sensor 201 may be a thermistor, or it may be a suitablealternative. A digital filter 203, such as a single-pole InfiniteImpulse Response (IIR) filter, has a response characterized by a thermaltime constant given in Table 0. The digital filter transforms a timesequence of immediate or raw sensor readings or values, for example fromthe RF temperature sensor, into effective or estimated temperatures(processed sensor values) relating to the target location, for example,the battery hot spot. Note that if the thermal time constant has beencorrectly determined, the time sequence of computed effectivetemperatures or processed sensor values (at the output of the digitalfilter 203) will have time response characteristics that are similar inprofile to the real temperatures of interest (namely those of locationB), though they may be different in terms of absolute value. It is theseeffective temperatures or processed sensor values, computed by thesignal processing operation defined by the thermal time constant, thatare then used to monitor the real thermal behavior of the targetlocation in any subsequent thermal management operation. For example, inFIG. 2B, a sample taken from the time sequence of processed sensorvalues is applied to a previously calculated look-up table 205, to finda matching, suggested thermal mitigation action (if any). Tables 1 and 2below are examples of such look-up tables. The look-up table may beimplemented as a data structure stored in memory.

In other embodiments of this invention, more sophisticated signalprocessing techniques may be applied within the digital filter 203, tocompute the effective temperatures or processed sensor values, includingbut not limited to multiple-pole filters or Finite Impulse Response(FIR) filters, in order to improve the correlation between the availablesensors and the real temperature of the target location.

In other embodiments of this invention, more sophisticated statisticalanalysis techniques may be applied to predict the real thermal behaviorof the target location—see FIG. 2C. As shown in that figure, the digitalfilter output of multiple sensors 201_1, 201_2, . . . (using multipledigital filters 203_1, 203_2, . . . ) are transformed through amathematical “thermal model” implemented by a temperature calculator204, into a final prediction of the temperature at the target location.Techniques to build this thermal model include, but are not limited to,Principal Component Analysis and Multiple Linear Regression. See alsoU.S. patent application Ser. No. 12/250,498 filed Oct. 13, 2008 that hasbeen assigned to the same assignee as that of the present application,for additional details concerning the particular approach taken in FIG.2C for estimating the temperature of the remote, target location.

Before describing various thermal management processes in detail,several components of the wireless communications device are nowdescribed and which may be viewed as controllable heat sources that maybe commanded to reduce their power consumption (pursuant to a suggestedthermal mitigation action obtained from the look-up table 205, see FIG.2B). First, there is the display screen backlight. A light emittingdiode (LED) backlight has the following characteristic: its light outputdecreases about in direct proportion to a decrease in its powerconsumption. However, the response of the human visual perception systemto light intensity is approximately logarithmic, in the sense that alarge increase in light intensity (e.g., a doubling of backlight power)is needed to achieve a relatively small improvement in perceivedbrightness. To take advantage of these characteristics, in oneembodiment of the thermal management process, the default backlightpower is set to, for example, about 50% of its maximum specified power.Thereafter, when there is a threshold thermal event, the backlight poweris reduced to an amount that yields about one half the perceivedbrightness by a human. This has been experimentally determined to beabout 20% of the maximum specified power of a typical LED backlight usedin handheld device applications such as cellular phones. Lowering thebacklight power further has been found to not result in an appreciabledecrease in the heat produced by the backlight, and in fact is likely tomake the display screen very difficult to see. This process helpsachieve a significant reduction in heat produced by the backlight,without significantly impacting the user's experience with the device.

Another component or function in the device 100 that may be commanded todrop its power consumption is the transmit rate of the cellular networktransceiver. For example, the device may have third generation, 3G,cellular network communications hardware and software that enable itsuser to surf the Web, check email, and download video at greater speeds.In that case, the device may reduce its 3G, High Speed Downlink PacketAccess, HSDPA, transmit rate or limit its RF output power in response toa thermal event.

A thermal management process in accordance with an embodiment of theinvention is now described in some detail, with reference to the flowdiagram of FIG. 5. The process can be used to control temperature in theexample multi-function portable communications device 100 that isdepicted in FIG. 3 and FIG. 4. FIG. 3 is an external view of the device,while FIG. 4 shows a few components of interest by revealing severallayers that make up the device. This device 100 may be an iPhone™ deviceby Apple Inc. Briefly, the device 100 has within its external case orhousing 102 the following components that operate together to providecellular phone, web surfing and digital media playback functions to itsuser: a CPU 404, a touch sensitive display screen 108 with a built-inbacklight, a cellular baseband processor 408, cellular network RFtransceiver PAs 409, 410, microphone 114, receiver (ear speaker) 112,speaker 122, and battery 404. Note that the display screen 108 need notbe touch sensitive; instead, user input may be had through a separate,built-in, physical keyboard or keypad (not shown). Additional tempsensors may be included, such as one that is associated with aSubscriber Identity Module, SIM card (not shown) or is on-chip with thebaseband processor 408 in the device 100.

The battery 404 is located at the rear of the device 100, in front of aback case or panel 104 which is part of the external case 102, while thedisplay screen 108 is at its front. The battery 404 faces the back faceof a printed wiring board (pwb) 419 on which the CPU 404, basebandprocessor 408, and PA 410 are installed. A separator panel 415 may beincluded for greater structural integrity and/or heat insulation,between the battery 404 and the board 419. The PAs 409, 410 in thisexample are soldered to the front face of the board 419. There are alsoseveral temperature sensors, including a board temp sensor 414 locatednear an edge of the motherboard or baseboard, an RF temp sensor 416located closer to the Pas 409, 410 than the board temp sensor 414, and abattery temp sensor 418 located closer to the battery 404 than either ofthe two other sensors. A thermal management program, stored in memory417, may be executed by the CPU or by another processor within thedevice, to perform some of the operations recited in FIG. 5.

Referring now to FIG. 5, beginning in the laboratory setting,statistical techniques and direct, instrumentation-type temperaturemeasurements of a target location of interest in the device are taken,versus simultaneously taken readings given by one or more temp sensorsthat are built-into in the device but that may be “remote” from thetarget location (block 504). A range of temperatures of interest arecovered, e.g. 40-70 degrees, by heating the device 100 from an externalsource and/or allowing the device 100 to heat up by virtue of its ownoperation. In addition, a suitable time interval is defined over whichthe measurements are taken (e.g., several minutes). A number ofspecimens of the same device 100 can be connected to the instrumentationcircuitry to take such measurements, and the resulting laboratory datais recorded for statistical analysis. A mathematical relationship maythen be derived from the recorded lab data, which relates one variablethat indicates the hot spot temperature, to another variable, namely thetemperature sensed by one or more temp sensors (block 508). Thisrelationship may have two aspects. First, there is the contribution bythe thermal time constant introduced above in connection with FIG. 1 andFIG. 2A, to obtain the “processed” curve. This aspect is reflected inoperation 509 in which digital filter coefficients are generated thatshape the time response of a digital filter so that the filter's outputmatches the envelope of the temperature vs. time behavior of the targetlocation, when its input is a sequence of temperature readings from oneor more remote sensors. The computed filter coefficients are then storedor encoded in the manufactured specimens of the device 100. Second, afurther relationship that makes an adjustment to the processed curve toobtain an estimate of the real temperature of the target location, isdetermined.

For example, consider a thermal management process that controls thetemperature of the battery's hot spot. It has been discovered that thehot spot of the battery 404 may be the part of the battery that isclosest to the PAs 409, 410. Instrumentation-based measurements of sucha battery hot spot reveal that whenever it is near or in its maximumtemperature range (as specified by, for example, the battery'smanufacturer), this is generally due to the heat produced by the PAs409, 410, which are located nearby. Thus, a better indicator of thebattery hot spot temperature (in the absence of a temp sensor that justhappens to be located at the battery hot spot) may actually be the RFtemp sensor 416, which may be the sensor that is closest to andassociated with the power amplifiers, PAs 409, 410. An even betterindicator of the battery temperature is the processed version of theoutput of RF temp sensor 416, i.e. a sequence of temperaturemeasurements made by the RF temp sensor 416 that has undergone digitalsignal processing designed to track the actual rise and fall in batterytemperature. Such a digital filter may be defined in operation 509.

To obtain a relatively accurate estimate of the target location'stemperature, a further mathematical relationship may be needed (e.g., toconvert the “processed” curves of FIGS. 1-2A into estimates of the realtarget location temperature. In one case, a linear relationship betweenthe two temperatures may be derived, in the form of,

Battery hot spot=K1+K2*processed_(—) RF_temp_sensor   (equation 1)

where K1 and K2 are constants that are selected to best fit a curve(here, a straight line) to the experimental data representing the actualbattery hot spot temperature. Thus, adjusting the processed RF tempsensor output in this manner is revealed to be a reasonably reliablepredictor or estimator for the actual battery hot spot temperature,during field use of the device. This means the battery temp sensor (ifone is used) need not be located at the hot spot.

In one embodiment of the invention, once the temperature relationship(equation 1) between battery hot spot and processed RF temp sensor hasbeen determined in this manner, it may be reflected in a predefinedlookup table stored in the memory 417 of the device 100 (block 512). Thetable associates or maps a list of battery hot spot temperatures ofinterest, e.g. those that are in a band at or near the maximumtemperature specified by the battery's manufacturer, to processed RFtemp sensor thresholds (in accordance with the predefined relationship).In addition, for each threshold (also referred to as a thermal event ortemperature limit), the table lists a respective power consumptionchange command or function limit, to be issued in the device in responseto the threshold being reached, to mitigate a thermal situation. For agiven threshold, a corresponding blank entry in the Special Actioncolumn refers to a “no change” command, i.e. no change to the powerconsumption of the components in the device is needed. See for instanceTable 1 below. Note each threshold value in the table may actuallyrepresent a respective, band or range of temperature values that definethe thermal event. The relevant column here is the “Processed RF PASensor Threshold” column, which reflects the thermal time constant of atarget location, e.g. the battery hot spot, relative to a temperaturesensor located at the RF power amplifiers.

TABLE 1 Special Action Processed Processed (power RF PA Batteryconsumption Notification Range Sensor Sensor change Level PercentageThreshold* Threshold# command) 0 0% 57.92 C. 51.80 C. 1 13% 58.02 C.51.97 C. 2 23% 58.06 C. 52.88 C. 3 25% 59.13 C. 53.72 C. 70% Backlight 432% 59.60 C. 54.47 C. 5 41% 60.07 C. 55.22 C. 50% Backlight 6 49% 60.49C. 55.88 C. 7 56% 60.85 C. 56.46 C. 8 63% 61.22 C. 57.05 C. 9 69% 61.54C. 57.55 C. 10 74% 61.80 C. 57.95 C. 11 80% 62.11 C. 58.46 C. 12 84%62.32 C. 58.80 C. Kill Applications 13 89% 62.58 C. 59.21 C. 14 93%62.79 C. 59.55 C. 15 97% 63.00 C. 59.88 C. 16 100% 63.16 C. 60.13 C.Sleep *Correlated to battery hot spot #Correlated to back case/panel

Table 1 may be used in-the-field, as follows—see blocks 516-524 of theflow diagram in FIG. 5. Note that unless otherwise specified, the orderin which the operations or steps of a process can occur is not limitedto that which is shown in an associated flow diagram. Referring now tothe flow diagram in FIG. 5, consider a reading taken from the RF tempsensor in the field and that has been processed in accordance with athermal time constant associated with a target location (block 516).This single reading may be sufficient to index into the look up table,to determine what power consumption action to take; alternatively, itmay be combined with a reading from one or more other temp sensors.Table 1 above indicates that once the processed RF temp has risen to acertain level, a particular action should be taken with respect to acertain component of the device. The table shows how to respond toprogressively rising RF temp sensor readings. As the processed RF tempsensor rises to indicate about 59.13 degrees, the backlight is dimmed to70% of its maximum power level. As the temperature continues to risefrom there, the backlight is further dimmed to 50%. Eventually, thetable indicates when most if not all applications executing in thedevice will be killed, as the temperature continues to rise. Finally,when a hot limit of the device is near, the table indicates that it istime to put the device into a low power sleep state. Thus, moregenerally, the temperature reading from a given temp sensor is used toindex into the table, to thereby identify a power consumption actionassociated with a component of the device 100 (block 520). Next, theidentified power consumption action is applied to the component (block524), to achieve the expected change in thermal behavior of the device100.

Note that the temperature threshold numbers in the tables here are onlyone instance of how each table can be populated. In addition, thethreshold value is approximate, in that that there is a tolerance bandaround each value. The more general concepts described here are ofcourse not limited to the specific numbers in any given table.

Also, the look-up table, which may be stored as part of thermalmanagement software in the device 100, need not list all of the columnsof Table 1. For example, the table may only list the (previouslycomputed) temp sensor values and their respective power consumptionactions, as correlated to real target location temperatures. The processin that case works by indexing directly into the look-up table, using aprocessed temp sensor reading. This may be viewed as the temp sensordomain embodiment. If desired, the estimated target location temperaturecan be obtained by plugging the processed temp sensor value intoequation 1.

An alternative to working in the temp sensor domain is to work in thetarget location domain. In that case, the look-up table stored in thedevice 100 need only list the target location temperatures (and theirrespective power consumption actions). The process would then work byfirst plugging the processed temp sensor reading into equation 1, andthen directly indexing into the look-up table with the computed orestimated target location temperature.

In accordance with another embodiment of the invention, a thermalmanagement process (that can be executed in the device 100) controls thedevice's external case temperature. For such a process, the targetlocation in the flow diagram of FIG. 5 becomes for example the center ofthe back case or panel 104 of the device 100. The in-the-field deviceportion of this process (namely blocks 516-524) may be executed inparallel with the battery hot spot process described above. Here, it hasbeen discovered that the battery temp sensor output may be a reasonablyreliable predictor for the external case temperature, particularly inthe example device 100 depicted in FIG. 4. Experimental measurements andstatistical techniques have yielded the following linear relationshipbetween the temperatures of the processed battery temp sensor (processedin accordance with the thermal time constant given in Table 0 above) andthe center of the back panel of the external case,

Back case center=K3+K4*processed_batt_temp_sensor   (equation 2)

where K3 and K4 are constants that are selected to best fit a straightline to the experimental data representing the actual back case centertemperature. This relationship may be used to fill in the processedbattery temp sensor values in the column identified by the same name, inTable 1 above. Here, the backlight is dimmed to 70% while in effectmonitoring the back case panel, when the processed battery temp sensorreading is about 53.72 degrees. In contrast, when monitoring the batteryhot spot through the processed RF PA temp sensor, the same dimmingaction occurs at about 59.13 degrees.

The above-described thermal management processes (in connection withTable 1) gave as examples several power consumption change commands forthermal mitigation, including backlight dimming, killing applications,and forcing the entire device 100 into a low power sleep state. Table 2below gives an example of another thermal mitigation action, namely thatof limiting RF transmit power. That table shows a list of battery hotspot temperatures of interest, mapped to corresponding processed RF PAtemp sensor readings (using the predefined relationship obtained fromexperimental data), and the corresponding RF output or transmit powerlimits that are to be placed on the RF PA 409, 410 (see FIG. 4). Table 2may be used by another thermal management process that is running in thedevice, in parallel with those described above in connection withTable 1. Table 2 describes how to limit the transmit power as a functionof battery hot spot temperature, the latter having been correlated tothe RF PA temp sensor which is being monitored.

TABLE 2 Change command Processed RF PA Sensor (RF Transmit Power BatteryHot Spot Threshold Limit) 59.00 C. 59.22 C. 24.000 dBm 59.33 C. 59.52 C.23.625 dBm 59.64 C. 59.79 C. 23.250 dBm 59.93 C. 60.04 C. 22.875 dBm60.20 C. 60.27 C. 22.500 dBm 60.53 C. 60.56 C. 22.000 dBm 60.82 C. 60.81C. 21.500 dBm 61.09 C. 61.05 C. 21.000 dBm 61.33 C. 61.26 C. 20.500 dBm61.60 C. 61.49 C. 19.875 dBm 61.84 C. 61.70 C. 19.250 dBm 62.09 C. 61.92C. 18.500 dBm 62.30 C. 62.11 C. 17.750 dBm 62.51 C. 62.29 C. 16.875 dBm62.69 C. 62.45 C. 16.000 dBm 62.86 C. 62.60 C. 15.000 dBm 63.00 C. 62.72C. 14.000 dBm

Thus, combining two processes associated with Table 1 and Table 2 yieldsthe following example scenario. When the processed RF PA temp sensordata, as correlated to the battery hot spot, indicates about 60.27,Table 1 suggests dimming the backlight to 50% while Table 2 suggestslimiting the RF transmit power to 22.5 dBm. One or both of these thermalmitigation actions are then taken (FIG. 5, operation 524).

A further thermal management process is now described that may also berunning in parallel with those described above. This process accessesTable 3 (see below) while effectively monitoring the back casetemperature, based on the previously determined temperature relationshipthat correlates the back case temperature with processed battery tempsensor data (here, thermistor output data). In this process, the powerconsumption mitigation action taken at a given temperature thresholdincludes limiting the RF transmit power to the specified level. Forexample, according to Table 3, the RF transmit power of the device 200shall not be allowed to increase above 21 dBm when the processed batterytemp sensor data (as correlated to the center of the back case) isindicating about 56.79 degrees.

TABLE 3 Processed Battery Change command Back Case Center ThermistorLimit (RF PA Tx Limit) 48.00 C. 53.89 C. 24.000 dBm 48.23 C. 54.20 C.23.750 dBm 48.44 C. 54.50 C. 23.500 dBm 48.64 C. 54.78 C. 23.250 dBm48.84 C. 55.05 C. 23.000 dBm 49.02 C. 55.31 C. 22.750 dBm 49.20 C. 55.55C. 22.500 dBm 49.45 C. 55.90 C. 22.125 dBm 49.68 C. 56.22 C. 21.750 dBm49.89 C. 56.51 C. 21.375 dBm 50.09 C. 56.79 C. 21.000 dBm 50.27 C. 57.04C. 20.625 dBm 50.49 C. 57.35 C. 20.125 dBm 50.70 C. 57.64 C. 19.625 dBm50.92 C. 57.95 C. 19.000 dBm 51.16 C. 58.28 C. 18.250 dBm 51.40 C. 58.61C. 17.375 dBm 51.62 C. 58.92 C. 16.375 dBm 51.82 C. 59.20 C. 15.250 dBm52.00 C. 59.44 C. 14.000 dBm

As the back case becomes “too hot”, for example during a phone call madewhen the device has been left inside a car in the sun for a few hours,the RF transmit power might have to be limited to such a low level(based on Table 3), that the cellular base station tower with which thedevice 100 is communicating may decide to drop the ongoing phone callor, if possible, initiate a smooth hand over of the call from, forexample, a 3G cellular network to one that uses lower (overall) RFpower, e.g. a 2G network. Slowly reducing the available transmit powerin the manner shown in Table 3 may be a better option than the device100 itself deciding to drop the call altogether (e.g., by killing acellular phone application that is running). Reducing the availabletransmit power gradually as indicated in Table 3, while allowing anongoing call to continue even as the device gets hotter, will give thecellular network a chance to hand over the call to another wirelesscellular network communications protocol that calls for lower powerconsumption in the device 100.

Note that in some cases, such as in a 3G cellular network, the celltower may be continuously or repeatedly commanding each of the phoneswith which it is communicating to adjust their respective RF transmitpower levels during phone calls (e.g., as a particular phone movescloser to or farther from the cell tower, or as the number of activephone calls being handled by the cell tower changes). In some cases,there may be a conflict between the command from the cell tower and thecommand in Table 3, e.g. the cell tower may demand more power, whileTable 3 requests a reduction (due to increasing, processed battery tempsensor readings). In that case, Table 3 may override the cell tower'srequest for greater power.

In other cases, the cell tower may signal the device 100 to reduce itstransmit power level, even while Table 3 allows a higher limit. In thosesituations, the device may prefer to operate at the lower level.

Hysteresis may be incorporated into the thermal management processesdescribed above. For example, with hysteresis, as the device cools offand the temp sensor readings drop, a higher power consumption command orlimit (indicated in one of the tables above and that is associated withthe new lower temperature level), is not resumed immediately. Rather,the process delays resumption of the higher power consumption level, tofor example ensure that the device is in fact cooling off at asufficiently high rate. For instance, hysteresis may require that theprocessed temp sensor reading further drop by about ½ degree, relativeto one of the threshold levels indicated in the table, before the higherpower consumption associated with that threshold level is resumed orpermitted.

In addition to the processes described above, the device 100 may alsohave a fail-safe process or mode in which several components of thedevice (e.g., cellular network PA, backlight, music playerfunctionality) are essentially shut down due to excessive temperature.For example, the fail-safe mode may be entered when there is a thermalevent that risks violating the predefined maximum battery temperaturerange, e.g. beyond 63 degrees.

As a precursor to the fail-safe mode, the device 100 may have a processthat first alerts the user, by showing a graphic on the display screen108, when a temperature limit that is near a hot limit (or other maximumspecified operating temperature of the device) has been reached. Forexample, the battery hot spot may be at its manufacturer specifiedmaximum, or the back case center may be at a UL specified maximum orother maximum user comfort temperature. This allows the user himself tothen immediately end the call for example, or shut down a particularlypower-hungry application that may be running. Alternatively, the processcould automatically invoke a reset and/or reboot of the entire deviceand its operating system. This might be able to alleviate the hightemperature situation, assuming that it has been caused by a problemwithin the device (e.g., a defective software routine or a defectivepiece of hardware). If following completion of the reset/reboot thedevice does not cool off, despite certain power hungry applications nolonger running being active, then the entire device 100 may beautomatically shut down. This reflects an understanding, by the thermalmanagement processes, that the current thermal situation in the devicelikely has external causes beyond its control.

So far, various thermal management processes have been described whichmay be based on indexing into a look up table, using either a processedtemp sensor reading or a further correlated value that represents theactual temperature of the target location, to determine what powerconsumption action to take in the device. It should be understood thatthe look up table is thus said to correlate temp sensor readings withthe expected, actual temperature of a remote, target location. Howeverin doing so, the look up table need not actually contain a list ofeither of those values. For example, Table 1 above lists only processedRF PA temp sensor values, not raw sensor readings (and one or moreassociated power consumption actions, “Special Actions” column, that aresuggested to mitigate, e.g., reduce, the actual temperature of thetarget location at selected temperature thresholds). As an alternative,the list of processed readings could be mapped to (and replaced with)their corresponding, computed target location values. See for exampleequation 1 which gives the computed temperature values of the batteryhot spot, based on processed RF PA temp sensor readings.

One or more of the above-described thermal management processes can runin parallel, to control the power consumption of various components ofthe device simultaneously, based on information obtained from the sametemp sensors. Other than when using the hysteresis effect mentionedabove, these processes need not have any memory of for example how long(time wise) a particular processed temp sensor variable has beenindicating above a given threshold. See FIG. 2B, showing the “open loop”nature of the process. In addition, they do not actually regulate thetemperature of a given part of the device, to ensure that it stays in anarrow, target range. Rather, they respond to temperature changes(according to the tables) across a relatively broad range. For instance,Table 1 covers the ranges 57-64 degrees and 51-61 degrees, the range forTable 2 is 59-63 degrees, and the range for Table 3 is 53-60 degrees.

In another embodiment of the invention, a regulating closed loop thermalmanagement process (that runs in the device) regulates the temperatureof a target location within a relatively narrow temperature range, basedon taking readings from one or more remotely located temp sensors in thedevice 100. For instance, a suitable, relatively narrow, battery hotspot temperature range may be 62-64 degrees. In general, this batterytemperature band should be not too high as to significantly reduce thelife of the battery (or render the external case too hot), and not toolow to render inefficient operation given the battery chemistry. Aprocess that can maintain this narrow temperature is depicted in FIG. 6.

Referring now to FIG. 6, a sample, processed reading is taken, from asequence of such readings taken from a remotely located temp sensor inthe device 100 (block 604). The sequence of readings had been processed,so that they correlate better with the temperature behavior of a targetlocation. Next, the sample, processed reading is further correlated withthe temperature of the target location (block 608). The latter may beperformed in part by inserting the processed temp sensor value into apreviously defined equation (e.g., one of the linear equations describedabove), that actually computes an accurate estimate of the correspondingtarget location temperature. The computed target location temperature isthen compared to the suitable, battery hot spot range (block 612) todetermine an error. If the error is not small enough (block 613), thenone or more of several predefined, power consumption actions that wouldreduce the error are selected and applied (block 616). The expectationis that this application of power consumption actions will correct thetarget location's temperature, back into the suitable range.

In some cases, a temp sensor's behavior history, and/or a thermal timeconstant associated with the sensor, has been stored in memory of thedevice, either by itself or correlated to that of a target location.This information can be consulted, e.g. as part of block 616, to furtherdetermine for example the strength of the power consumption action thatwill be taken. For instance, if the back case center has been steadilycooling for the past 30 seconds (as indicated by monitoring the batterytemp sensor for example), even though the back case center is stillabove its suitable temperature range, the limit on RF transmit power ofthe device 100 should be reduced only slightly, as compared to thesituation where the back case center has been fluctuating (rather thansteadily cooling) above its suitable range.

An embodiment of the invention is an electronic device comprising:

means for sensing a temperature of the device (e.g., thermistor builtinto the device;

means for correlating temperature of the sensing means with temperatureof another location in the device, in terms of what power consumptionaction to take for a given temperature of the sensing means that hasbeen correlated to a corresponding temperature of said another location(e.g., a look up table stored in the device that includes a list of tempsensor values and/or a list of target location temperatures, plus theirrespective power consumption actions which have been selected managethermals at the target location);

means for accessing the correlating means to identify said powerconsumption action which is associated with a component in the device(e.g., software running in the device that processes the temp sensorreadings by a) indexing directly into a list of temp sensor values, orb) first converting the temp sensor readings and the indexing directlyinto a list of target location temperatures; and

means for applying the identified power consumption action to theassociated component of the device (e.g., software running in the devicethat signals a CPU, an RF PA, or a backlight to limit its powerconsumption even at the expense of reduced performance by thecomponent).

An embodiment of the invention may be a machine-readable medium havingstored or encoded thereon instructions which program a processor toperform some of the operations described above. In other embodiments,some of these operations might be performed by specific hardwarecomponents that contain hardwired logic. For example, the digital filter203 in FIG. 2B may be implemented entirely as a programmable logic arraycircuit, or entirely as a programmed data processor. Those operationsmight alternatively be performed by any combination of programmedcomputer components and custom hardware components.

A machine-readable medium may include any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer), not limited to Compact Disc Read-Only Memory (CD-ROMs),Read-Only Memory (ROMs), Random Access Memory (RAM), and ErasableProgrammable Read-Only Memory (EPROM).

The invention is not limited to the specific embodiments describedabove. For example, the temperature threshold numbers in the tables hereare only one instance of how each table can be populated. In addition,the threshold value is approximate in that that there is a toleranceband around each value. The more general concepts described here are ofcourse not limited to the specific numbers in any given table.Accordingly, other embodiments are within the scope of the claims.

1. A method for thermal management of an electronics device, comprising: monitoring the temperature of a target location in the device without having a temperature sensor at that location, by (a) filtering a sequence of temperature readings from a temperature sensor that is at a remote location in the device, and (b) using one of the filtered temperature readings to access a look up table, that lists temperature thresholds and corresponding power consumption commands, and thereby identify a power consumption command associated with a component of the device, wherein the corresponding power consumption commands include a plurality of no change commands and at least one change command that limits or reduces power consumption of a component in the device, wherein the look up table correlates temperature at the temperature sensor with temperature at said target location in the device.
 2. The method of claim 1 further comprising: repeating (b) so as to use another one of the filtered temperature readings to access the look up table, until said at least one change command is identified; and applying the identified change command to limit or reduce power consumption of a component of the device.
 3. The method of claim 1 wherein the list of temperature thresholds in the look up table refers to temperature at said target location of the device, and wherein using the filtered temperature reading to access the look up table comprises converting, using a predefined mathematical relationship, the filtered temperature reading into a value that refers to temperature at said target location.
 4. The method of claim 1 wherein the list of temperature thresholds in the look up table refers to filtered temperature readings, wherein using the filtered temperature readings comprises: directly indexing into the look up table with the filtered temperature reading.
 5. The method of claim 2 wherein applying the identified change command to the component of the device comprises: limiting RF transmit power of a cellular network transceiver in the device to a level that is indicated by the identified change command.
 6. The method of claim 2 wherein applying the identified change command to the component of the device comprises: reducing light output of a display screen backlight in the device to a level that is indicated by the identified change command.
 7. The method of claim 1 wherein applying the identified change command to the component of the device comprises: reducing clock frequency or supply voltage of a data processing unit in the device to a level that is indicated by the identified change command.
 8. A method for thermal management of an electronic device, comprising: reading a first temperature sensor that is located in the device near a first component of the device and far from a second component of the device; reading a second temperature sensor that is located in the device near the second component and far from the first component; and changing the limit on power output by the first component, in accordance with said reading the second temperature sensor.
 9. A method for thermal management of an electronic device, comprising: reading a first temperature sensor that is located in the device closer to a first component of the device than second and third components of the device; reading a second temperature sensor that is located in the device closer to the second component than the first and third components; and correlating readouts from the first temperature sensor with readouts from the second temperature sensor to extrapolate temperature of a selected one of the first, second and third components, and on that basis changing a power consumption limit of the selected component.
 10. An electronic device comprising: a temperature sensor; and a thermal manager having a digital filter whose input is to receive raw temperature values from the sensor and whose output is to provide processed temperature values according to a filter function that correlates temperature at the sensor with temperature at another location in the device, the thermal manager having a look-up table that further correlates temperature at the sensor with temperature at said another location, the look-up table having a list of temperature values, representing a temperature range at the sensor or at said another location, and a plurality of power consumption change commands associated with the list of temperature values, respectively, the thermal manager to access the look-up table a plurality of times, each time using a different one of processed temperature values, to identify a plurality of power consumption change commands and evaluate the identified plurality of power consumption change commands to determine what change, if any, should be commanded to the power consumption of a component in the device.
 11. The electronic device of claim 10 further comprising: a wireless communications transceiver RF power amplifier, wherein one of the identified power consumption change commands is an RF output power limit on the power amplifier.
 12. The electronic device of claim 10 further comprising: a display screen having a backlight, wherein one of the identified power consumption change commands is a brightness limit on the backlight.
 13. The electronic device of claim 10 further comprising: a central processing unit, CPU, wherein one of the identified power consumption change commands is a processor clock limit or supply voltage limit on the CPU.
 14. The electronic device of claim 10 wherein the thermal manager comprises memory in which is stored a history of temperature readings from the sensor that have been correlated to temperature of said another location, the thermal manager to consult the stored history and on that basis alter the strength of the change that is commanded to the power consumption of the component in the device.
 15. An electronic device comprising: a temperature sensor disposed at a first location of the device that is remote from a second location of the device; and a thermal manager to process a sequence of temperature readings from the temperature sensor to obtain a sequence of processed temperature readings, the thermal manager having a look up table that lists a plurality of temperature thresholds associated with a plurality of power consumption commands, respectively, wherein the power consumption commands include a plurality of no change commands and at least one change command that limits or reduces power consumption of a component in the device, the thermal manager to select a plurality of the processed temperature readings and use each selected processed reading to access the look up table and thereby identify a power consumption command, and to evaluate the identified power consumption command to determine what change, if any, should be commanded to mitigate a thermal event in the device.
 16. The electronic device of claim 15 wherein the second location is a location whose temperature behavior, in response to an input heat source at the first location, is substantially different than that of the first location.
 17. The electronic device of claim 15 wherein the thermal manager is to implement hysteresis such that as the device cools off, an identified power consumption command from the look up table that increases power consumption of a component in the device is not resumed immediately but rather is delayed until the device cools off further.
 18. The electronic device of claim 15 wherein the power consumption commands in the look up table include at least one that alerts a user of the device about temperature in the device, by showing a graphic on a display screen of the device.
 19. The electronic device of claim 15 wherein the plurality of temperature thresholds listed in the look up table are in the range 50-65 degrees Centigrade.
 20. An electronic device comprising: a temperature sensor disposed at a first location of the device that is remote from a second location of the device; and a thermal manager to process a sequence of temperature readings from the temperature sensor to obtain a sequence of processed temperature readings associated with the second location, the thermal manager to (a) select a plurality of the processed temperature readings and convert each selected processed reading into an estimate of temperature at the second location, (b) compare the estimate to a desired temperature for the second location to determine an error, and (c) evaluate the determined error to determine whether or not a predefined, power consumption action that would reduce the error needs to be applied.
 21. The electronic device of claim 20 wherein the desired temperature ranges up to two degrees Centigrade. 